Molecular Orientation of Phenyl Groups at Graphene/Polystyrene Interface

Blending graphene with polymer matrices is of great interest in designing nanocomposites with enhanced thermal and mechanical properties. The challenge is to avoid aggregation of these high surface area graphene sheets. Understanding the molecular interactions between graphene and polymer molecules is important to identify the correct chemistry needed to disperse these nanofillers. Here, we report the use of interface-sensitive sum-frequency generation spectroscopy (SFG), molecular dynamics (MD) simulations, and density functional theory (DFT) to study the orientation of polystyrene chains next to graphene/polystyrene interface. DFT provides information on molecular hyperpolarizability, whereas the MD simulations shed light on the orientation distribution of phenyl and methylene groups. The combination of MD and DFT is used to predict the SFG spectra of PS chains next to a graphene/polystyrene interface. In my presentation, we will compare SFG spectra calculated using MD/DFT with those measured experimentally using SFG. Further, we will discuss the need to independently obtain molecular orientation distributions using MD for correctly analyzing the SFG data.